Implement Client-side Validation For A Form

We have this long form in our website that was broken into steps like wizard. Some of the validation is handled by HTML5 builtin validation. The rest of the validation is handled server-side. We want to improve that and make the validation done at client side too to improve usability. So, the look-and-feel and user-friendliness are very important. Also, we want to refactor the existing jQuery code in the form and clean the mess there too.